ncat: process Stops in State T after some time

On 12.04, 15.10 and 16.04 I'm seeing consistent hangs of ncat when left running for some time.

In the particular scenario it is proxying a TCP connection as a background job using:

ncat -m 1 -6kl 10006 | ncat -kl 10007 &

When it stops I see (Here it's explicitly called within a sub-shell):

$ jobs
[4]+ Stopped bash -c 'ncat -m 1 -6kl 10006 | ncat -kl 10007'

$ ps -efly | grep ncat
T tj 26816 25874 0 80 0 2436 1296 - 17:42 pts/2 00:00:00 bash -c ncat -m 1 -6kl 10006 | ncat -kl 10007
T tj 26817 26816 0 80 0 1308 1166 - 17:42 pts/2 00:00:00 ncat -m 1 -6kl 10006
T tj 26818 26816 0 80 0 1288 1166 - 17:42 pts/2 00:00:00 ncat -kl 10007

$ sudo grep ^SigQ /proc/2781{7,8}/status
SigQ: 1/7982
SigQ: 1/7982

After attaching gdb to the first process it looks like it is stopped due to a SIGTTIN signal. Not sure why since the process stdin should be connected to the listening network socket.